Try fishing from a bridge on a tidal river, not the Merrimack but most coastal towns have smaller tidal rivers. My favorites are the Ogunquit River in Maine and North River in Marshfield. The baitfish, sandeels for example will flow in with the tide and the bass follow, and if the water is clear watch them swim an "S" like pattern under the bridge, always on the left side of the direction your facing. But, what you want to do, is cast and float your line on the side of the main current so it ends up on the sandbar where its calmer or has an eddy current. This area should easy to identify, and unlike the beach, the fish are always there.
Whether or not you catch one is up to you and nature. Stripers feed more actively at night, especially when the water temp warms up. I have friends who keep detailed journals and the data shows that the Moon phases and striper feeding are connected. Sometimes they are finicky and don't want what your serving, but atleast you got a shot. I start fishing in the spring in Newport RI and go up the coast to the Main by labor day weekend. Stripers prefer 58-63 degree water, so they move more north as it gets warmer and out to deeper waters during hot summer days, so if its warm, fish at night or atleast dusk or dawn when its cooler.
Live eels at night is a recipe for catching a keeper, and flowing in the current they stay lively for hours. If you can rake some sandeels up at low tide or jig with a treble hook if their by the bridge, this works best during the day. For chunk bait, go with fresh herring if possible, or find some quality frozen. They stink so bring some orange wipes or some waterless orange hand cleaner.
For a rig:
I recommend a baitrunner style reel such as my Shimano 8000D, a 1-3oz weight( depends on the rod) on a slider above the swivel with a flourocarbon leader and a circle hook, if you use a clam a rubber band helps keep it on the hook. If your using live eels, obviously go with no weight. Set your main drag fairly tight, flip your drag switch and set the drag very light with almost 0 resistence. This allows your line to flow with the current without opening your spool which or pulling with your hand, which lets it flow more naturally. If you cast out on to the bar or if your bait flows into an ebb area and stops moving, keep the same drag setting.
When you get a bite:
Let the fish start running with it and dont try to set the hook fast, let it run a good 50 yards and then turn your reel and engage the main drag and your circle hook ends up where it should be, and you can release a fish that will live to be caught again when its big enough to eat or if you choose to catch and release like many of us do.
I can't believe I just typed all that, but glad to help out and hope you can get a keeper or atleast have fun catching a bunch of lively schoolies.